This invention relates to alternator tuning devices, particularly to isolating decouplers using a torsion spring for isolation. The function and utility of isolating decoupler tuning devices is commonly known. A typical device comprises multiple components including an isolating spring, one way clutch, bearing(s), a pulley and other ancillary parts. The need for each of these components typically requires the overall diameter of the device to exceed what the industry desires. Decreasing automotive engine sizes and ever increasing fuel efficiency requirements indicate that isolating decoupler diameters can be an engine development limiting factor.
A size limiting relationship is that between the pulley and a torsion spring. In the prior art devices the torsion spring is typically in a radial “stack” disposed between the shaft and the pulley. This arrangement tends to increase the diameter of the pulley depending upon the spring rate of the torsion spring.
Representative of the art is U.S. Pat. No. 6,083,130, which discloses a serpentine belt drive system for an automotive vehicle comprising a drive assembly including an internal combustion engine having an output shaft with a driving pulley thereon rotatable about a driving pulley axis. A sequence of driven assemblies each has a driven pulley rotatable about an axis parallel with the driving pulley axis and a serpentine belt mounted in cooperating relation with the driving pulley and with the driven pulleys in a sequence which corresponds with the sequence of the driven assemblies when related to the direction of movement of the belt to cause said driven pulleys to rotate in response to the rotation of the driving pulley. The sequence of driven assemblies includes an alternator assembly including an alternator shaft mounted for rotation about a shaft axis. A hub structure is fixedly carried by the alternator shaft for rotation therewith about the shaft axis. A spring and one-way clutch mechanism couples the alternator pulley with the hub structure. The spring and one-way clutch mechanism comprises a resilient spring member separately formed from and connected in series with a one-way clutch member. The resilient spring member is constructed and arranged to transmit the driven rotational movements of the alternator pulley by the serpentine belt to the hub structure such that the alternator shaft is rotated in the same direction as the alternator pulley while being capable of instantaneous relative resilient movements in opposite directions with respect to the alternator pulley during the driven rotational movement thereof. The one-way clutch member is constructed and arranged to allow the hub structure and hence the alternator shaft to rotate at a speed in excess of the rotational speed of the alternator pulley when the speed of the engine output shaft is decelerated to an extent sufficient to establish the torque between the alternator pulley and the hub structure at a predetermined negative level.
What is needed is an isolating decoupler having a torsion spring with a diameter greater than a diameter of a belt bearing surface. The present invention meets this need.